The present invention relates to a first output position calculation method, a storage medium, a positioning device, and an electronic instrument.
The global positioning system (GPS) is widely known as a satellite positioning system, and is utilized for a car navigation system and the like. In the GPS, GPS satellite signals are respectively transmitted from a plurality of GPS satellites which orbit the earth, and a GPS receiver calculates (locates) its present position based on the received GPS satellite signals.
A GPS satellite signal affected by a multipath or the like may be included in the acquired GPS satellite signals. The term “multipath” refers to a phenomenon in which an indirect wave reflected or diffracted by a building or topography is superimposed on a direct wave from a GPS satellite so that the GPS receiver receives identical radio waves through multiple paths. Such a reception environment is referred to as a multipath environment. The present position may not be accurately calculated (located) when using a GPS satellite signal affected by a multipath. Specifically, it is necessary to perform positioning calculations while excluding a GPS satellite signal affected by a multipath or the like from the acquired GPS satellite signals. As a method of determining a GPS satellite signal affected by a multipath or the like, a method using an a priori residual (APR) has been known (see JP-A-2003-240836, for example).
A GPS receiver repeats positioning calculations each time a given period of time (e.g., one second) has elapsed, and outputs the calculated present position of the GPS receiver as the positioning result. About several seconds are normally required to output the first positioning result after starting positioning. A time to first fix (TTFF; time required to output the first positioning result) and positioning accuracy have a relationship in which the positioning accuracy decreases when giving priority to a reduction in TTFF and the TTFF increases when giving priority to an increase in positioning accuracy. Whether to give priority to an increase in positioning accuracy or a reduction in TTFF is determined depending on the reception environment. For example, it is desirable to give priority to an increase in positioning accuracy over a reduction in TTFF in a reception environment (e.g., multipath environment) with poor positioning accuracy so that the positioning result is output after the Z-count has been decoded and the positioning accuracy has been improved, even if the TTFF increases. On the other hand, priority may be given to a reduction in TTFF in an open-sky environment with high positioning accuracy so that the positioning result is output without waiting for the Z-count to be decoded.